1. Field of the Invention
The invention relates to power driven conveyors and more specifically to endless conveyors wherein the upper and lower runs of the same belt travel in vertically aligned, laterally bending paths. The invention also relates to endless conveyors having a carrier belt structure including pivotally interconnected rigid links, wherein separate pins interconnect links, the links pivoting about mutually perpendicular axes having interfitted ends.
2. Description of the Prior Art
Conveyors employing convoluted belts able to flex both horizontally and vertically are known for use in following a curved path, which may include horizontal curves, vertical curves, and spiral curves.
In one known embodiment which may be referred to as a "roller" type of flexible conveyor, such conveyors follow a path defined by a pair of channel shaped rails that are engaged by rollers or wheels that in turn carry the conveyor belt. The belt itself is constructed from a plurality of molded flexible pan sections that are longitudinally joined to define an endless belt of the desired length. The belt pans are carried on carriages, which may be joined to the belt at the junctions of the pan sections. Each carriage supports two pairs of rollers, one pair engaging each of the rails and having perpendicular axes to support the conveyor both horizontally and vertically. The carriages are joined by a standard link chain consisting of a series of generally ellipsoidal-shaped links, and the chain is used to pull the conveyor belt and carriages along the path defined by the rails. Roller type conveyors as described are taught in U.S. Pat. No. 2,701,050 and with further variation in U.S. Pat. No. 4,144,965.
The roller type of conveyor is well suited for moving heavy loads and for following a path wherein the curves are of relatively large radius and the elevation within the capability of the chain. The use of standard link chain to drive the conveyor places necessary limitations on conveyor design, such as limitations on the radius of acceptable curves and the degree of vertical rise. When the belt and chain twist, either deliberately to permit passage around a compound curve or accidentally because of an unbalanced load on a pan, the contact between links approaches a one-point, two-point, or line contact, resulting in high unit forces at those contact points, wear on the chain, and reduction in chain life. In order to gain an acceptable chain life, the link chains are surface hardened, which is a difficult process to accomplish well. Also, in order to prevent the pans from tilting too much under unbalanced load, the rails are widely spaced. Consequently, the carriages must be large to span the distance between the rails. The weight of such large carriages in turn limits the maximum elevation to which the conveyor can rise because the weight of the moving parts plus the load will exceed the allowable weight on the chain.
The curvature of the conveyor path with roller-type conveyors is also limited by the chain tension when a link chain is employed. Specifically, the roller force against the rails limits the acceptable curvature, as roller forces are directly proportional to the chain tension and the distance between rollers and are inversely proportional to the radius of the curve and the number of rollers in contact with the rail. While a closer carriage spacing would reduce roller force, it would increase overall conveyor weight and reduce maximum elevation of the run. Design experience has shown that the advantages of lowering conveyor weight and reducing cost outweigh the benefits of closely spacing the carriages so as to permit small radius curves in the conveyor track; and hence, the roller type of flexible belt conveyor is best suited for wide radius curve applications because of chain tension limitations.
Another known embodiment of such conveyors which may be referred to as a "slide" type of flexible conveyor, the conveyor path is defined by a central slide channel that is engaged with the actual conveyor chain. This chain is of special design and is formed from alternating double and single vertical bar links that are joined by cross pins having a loose fit. Twisting of this type of chain produces high unit forces between the pin and bar links, and again the chain is surface hardened to increase chain life. Excessive tipping of the conveyor belt and excessive twisting of the chain are prevented by the presence of side flanges associated with the central channel and side skids or rollers associated with the belt. The skids are positioned to strike the flanges before tipping becomes so great that the load is lost from the belt or the chain is twisted beyond the maximum acceptable degree. Such a conveyor is taught in copending U.S. patent application No. 74,345.
The slide type of conveyor has a larger friction factor than the roller type, and the chain tension of the slide type increases in curves more rapidly than that of the roller type. However, the conveyor forces against the central channel in the slide type are distributed over a large surface area, resulting in very low wear on the slide surfaces. The slide type conveyor finds best application with lighter loads as compared to the capability of roller type conveyors, and the combination of track elevation, curvature, and length must be kept within the limitations of the chain. In both roller and slide conveyors, an intermediate drive would remove many of these limitations. However, a practical, reliable intermediate drive for use with either of the types of chains used in the prior art conveyors is not yet known.
Although both the roller and slide types of conveyors are capable of similar serpentine twisting, as explained above, these two types of conveyors are best suited for different load ranges, and both types must observe practical limitations on conveyor length, elevation, and degrees of curvature. It is desirable to create a conveyor having load handling capabilities intermediate to the capabilities of the above described slide and roller type conveyors, and having the capability to negotiate many degrees of curvature and long lengths.
A conveyor of this description is proposed in U.S. Pat. No. 3,934,708, wherein a rectangular rail contains the chain, carriages and rollers therein. The carriages of this design may be light in weight and the rollers may be clamped to every other link of the chain for roller spacing equal to the length of each conveyor belt pan. However, the chain in this construction continues to be standard link chain formed from alternating vertical and horizontal ellipsoidal chain links. The roller axes must in this design be between the pivot points of the links, and the links will have point-contact or line-contact on some curves. Because the carriage is on and around the alternating chain links, the carriage will approach close to the pivot point of the chain on curves and, thus, the radius of turn is limited. Further, drive and idler sprockets have their teeth riding between the side of the chain's horizontal links and apply concentrated pressure against the load-bearing links. Still another unresolved problem with this structure is that in those embodiments having both horizontal and vertical rollers in the same carriage, one type of such rollers is proposed to be inside the other, so that the vertical rollers are a different size than the horizontal rollers.
The conveyor chain utilized in the present invention, as will be described in greater detail, has been used in overhead monorail systems wherein the chain supports depending hangers that, in turn, carry a load. This chain is a product of Millers Mechanical Equipment Ltd., New Zealand. The present invention relates to a special adaptation of this chain for operation with a conveyor belt carrying a load positioned over the chain. The above noted problems of the prior art are overcome by creation of a belt or pan conveyor that is now able to follow a serpentine path having a large degree of curvature and long length, as described below.